This invention relates to apparatus for controlling the operation of internal combustion engines and more particularly to apparatus for controlling the ratio of air to fuel in a mixture to be combusted in such an engine.
The control of emissions from internal combustion engines and particularly automobile engines has become a major environmental concern. Various federal and state regulatory agencies have promulgated emission standards for certain substances found in the combustion products entering the atmosphere through an engine's exhaust, the most important of these substances being hydrocarbons, carbon monoxide and oxides of nitrogen. To meet emission control standards, various pollution control devices such as catalytic converters and thermal reactors have been developed for use with automobile engines to reduce the quantities of unwanted substances emitted into the atmosphere to within prescribed limits.
It has been found that most efficient removal of unwanted substances by pollution control devices is achieved when an engine is operated within a narrow range of air-fuel ratio values for an air-fuel mixture combusted in an engine. Consequently, numerous systems have been developed which attempt to maintain the air-fuel ratio of a mixture to be combusted in an engine within this value range. Examples of systems of this type are disclosed in U.S. Pat. Nos. 3,939,654, 3,946,198, 3,949,551 and 3,963,009. While the systems disclosed in these patents do tend to keep the air-fuel ratio for a mixture to be combusted within the value range where maximum efficiency in removal is obtained, this is usually accomplished only by constantly adjusting the air-fuel ratio. Further, overadjustments frequently occur which then require additional corrections and the systems respond to transitory changes in an engine's operating characteristic to make adjustments when none are actually needed.